Note 6 - Warrants - Warrants Outstanding (Details) - USD ($)		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021
Balance, outstanding (in shares)		36,765,502	32,980,989
Issued (in shares)		19,604,796	7,088,094
Expired (in shares)		(4,016,754)	(1,046,528)
Balance, aggregate intrinsic value	[1]	$ 741,000
Balance, outstanding (in shares)		52,353,544	39,022,555
Minimum [Member]
Balance, outstanding, price range (in dollars per share)		$ 0.16	$ 0.16
Granted, price range (in dollars per share)		0.20	0.14
Expired, price range (in dollars per share)		0.19	0.19
Balance, outstanding, price range (in dollars per share)		0.14	0.14
Maximum [Member]
Balance, outstanding, price range (in dollars per share)		1.00	1.00
Granted, price range (in dollars per share)		0.29	0.26
Expired, price range (in dollars per share)		0.48	0.35
Balance, outstanding, price range (in dollars per share)		1.00	1.00
Weighted Average [Member]
Balance, outstanding, price range (in dollars per share)		0.27	0.29
Granted, price range (in dollars per share)		0.24	0.20
Expired, price range (in dollars per share)		0.35	0.24
Balance, outstanding, price range (in dollars per share)		$ 0.25	$ 0.27

[1] Aggregate intrinsic value based on closing common stock price of $0.18 at June 30, 2022